The observation and analysis of the true and vibronic false origins of the 3p Rydberg <- X transitions of cyclopentadiene revealed by polarization- selected two-photon resonant multiphoton ionization spectroscopy has enabled absolute assignments to be made for these transitions. Based on these assignments, the energies of the transitions, and previously reported or literature values for the energies of the 3p Rydberg <- X and valence transitions of butadiene and benzene, an empirical determination of the extent of interstate coupling was made for s-cis and s-trans dienes. The results are essentially none for the s-cis conformer and about 25% for the s-trans conformer. These results support theoretically calculated values of these interactions. A new research project on the dynamics of the photochemistry of dienes has been initiated.